This invention relates to a semiconductor device having a silicon oxide film as an insulating oxide film.
A thin silicon oxide film which is formed on the surface of a silicon wafer plays a fundamentally important part in the fabrication of a device such as an IC and an LSI device. In order to improve the following fundamental characteristics of the semiconductor device in a gate oxidation step, i.e., one of the important steps of thermal oxidation, such as
(1) the inclusion of an impurity such as mobile metal ions in the silicon oxide film,
(2) lowering the level of silicon oxide film to silicon interface,
(3) a high dielectric breakdown strength and a small variation in an interface level N.sub.SS,
(4) a uniform thickness, greater efforts have been made to purify a silicon wafer and an oxidating furnace.
It is evident that, of the impurity ions in the silicon oxide film as indicated by (1), the alkali metal ions such as sodium (Na) and potassium (K) act as mobile metal ions in the silicon oxide film to degrade the characteristics of the silicon oxide film.
The behavior of metals, other than the alkali metal, in the silicon oxide film is unclear on numerous points, There is a possibility that those elements taken in the silicon oxide such as iron (Fe), aluminium (Al), copper (Cu), chromium (Cr), nickel (Ni) or zinc (Zn) will improve the characteristics of the silicon oxide film.